I lasted about 15 minutes in Tim Hecker last night in Leeds. Turning all the lights off, pumping the room full of dry ice, and standing in relative discomfort whilst someone noodles on a laptop does not constitute a gig to me. Don't think I've ever left a gig so early, particularly one I was really looking forward to. Felt a bit ripped-off of my £12, would have been far better staying at home and listening to the records.
What have you left early? Bonus points if it's something you were looking forward to.